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Problem with the ADL5243 VGA


We bought an evaluation board ADL5243 EVAL from Analog. We want to use it as the AMP1-DSA-AMP2 mode. We used two cables to connect amp1out with DSA in, DSAout with amp2in respectively, then we measured the gain of the VGA with a VNA. We found that the gain is pretty unflat (please see the attached figure). Therefore, we wonder if we have missed something.

In the data sheet for ADL5243, it is written that "When configuring the ADL5243 evaluation board in the AMP1-DSA-AMP2 loop, remove Capacitors C1, C4, C5, and C8 and remove Resistor R10. Place 10 pF in place of C24 and C6, and 0 Ω in place of R32 and R33. If needed, placing a shunt capacitor (1.3 pF) at the output of the DSA improves the output return loss of this loop as described at the ADL5243 Loop Performance section. "

Do we need to do this or the evaluation board has already been configured in such a mode?

Thank you.



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